Cantilever probes for high speed AFM

Since the invention in 1986 atomic force microscopy (AFM) has become the most widely used scanning probe microscopy (Binnig et al. in Phys Rev Lett 56:930–933, 1986). The microscope images the interaction of forces like Van der Waals or Coulomb forces between a sample and the apex of a small tip integrated near the free end of a flexible cantilever. But as all other scanning probe techniques the AFM requires serial data acquisition and suffers therefore from a low temporal resolution. Enhancing the speed to video rate imaging makes high demands on scanner technology, control electronics and on the key feature the cantilever with integrated sharp stylus. For the cantilever probes, fundamental resonance frequencies in the MHz regime are envisaged while the force constant of a few nN/nm shall be maintained. We present different novel AFM probes with ultrashort cantilevers and integrated sharp tips for high speed AFM while focusing on widely dispersed applications and on aspects of mass fabrication.     

Design principle of micromechanical probe with an electrostatic actuator for friction force microscopy

It is important to understand friction force in micro/nano mechanical devices both at high sliding speed and with high lateral resolution. Dual-axis friction force microscopes that can provide high lateral resolution and accuracy have been proposed; however, the sliding speed is limited by the probe scan speed. While a micro mechanical probe (MMP) with an electrostatic actuator can overcome this problem, details of probe design have not been established yet. This paper presents the principle of the mechanical design for an MMP with high force sensitivity and sufficient drive force. The dimensions of the double cantilever beam control the spring constants, resonant frequencies, and drive force. The use of an actuated MMP enables accurate friction force microscopy at high sliding speeds, which is required for the design of micro/nano mechanical devices.     

Design optimization of high performance tapping mode AFM probe

Microsystem Technologies - To enhance the measurement performance of tapping-mode atomic force microscopy (TM-AFM), it is highly desirable that the TM-AFM probe has high resonant frequency and...     

Application of the differential transformation method to bifurcation and chaotic analysis of an AFM probe tip

The AFM (atomic force microscope) has become a popular and useful instrument for measuring intermolecular forces with atomic resolution, that can be applied in electronics, biological analysis, and studying materials, semiconductors etc. This paper conducts a systematic investigation into the bifurcation and chaotic behavior of the probe tip of an AFM using the differential transformation (DT) method. The validity of the analytical method is confirmed by comparing the DT solutions for the displacement and velocity of the probe tip at various values of the vibrational amplitude with those obtained using the Runge–Kutta (RK) method. The behavior of the probe tip is then characterized utilizing bifurcation diagrams, phase portraits, power spectra, Poincaré maps, and maximum Lyapunov exponent plots. The results indicate that the probe tip behavior is significantly dependent on the magnitude of the vibrational amplitude. Specifically, the tip motion changes first from subharmonic to chaotic motion, then from chaotic to multi-periodic motion, and finally from multi-periodic motion to subharmonic motion with windows of chaotic behavior as the non-dimensional vibrational amplitude is increased from 1.0 to 5.0.     

Resonant Magnetic Field Sensor With Frequency Output

This paper presents a novel type of resonant magnetic field sensor exploiting the Lorentz force and providing a frequency output. The mechanical resonator, a cantilever structure, is embedded as the frequency-determining element in an electrical oscillator. By generating an electrical current proportional to the position of the cantilever, a Lorentz force acting like an additional equivalent spring is exerted on the cantilever in the presence of a magnetic field. Thus, the oscillation frequency of the system, which is a function of the resonator's equivalent spring constant, is modulated by the magnetic field to be measured. The resonant magnetic field sensor is fabricated using an industrial CMOS process, followed by a two-mask micromachining sequence to release the cantilever structure. The characterized devices show a sensitivity of 60 kHz/Tesla at their resonance frequency$f_0= 175~ kHz$and a short-term frequency stability of 0.025 Hz, which corresponds to a resolution below 1$~mu T$. The devices can thus be used for Earth magnetic field applications, such as an electronic compass. The novel resonant magnetic field sensor benefits from an efficient continuous offset cancellation technique, which consist in evaluating the frequency difference measured with and without excitation current as output signal. 1676     

Optimal shapes of parametrically excited beams

Straight elastically supported beams of variable width under the action of a periodic axial force are considered. Two shape optimization problems for reducing parametric resonance zones are studied. In the first problem, the minimal (critical) amplitude of the excitation force is maximized. In the second problem, the range of resonant frequencies is minimized for a given parametric resonance zone and a fixed amplitude of excitation. These two optimization problems are proved to be equivalent in the case of small external damping and small excitation force amplitude. It is shown that optimal designs have strong universal character, i.e. they depend only on the natural modes involved in the parametric resonance and boundary conditions. An efficient numerical method of optimization is developed. Optimal beam shapes are found for different boundary conditions and resonant modes. Experiments for uniform and optimal simply supported elastic beams have been conducted demonstrating a very good agreement with theoretical prediction.     

Nanofabrication of solid surface using probe oxidation

Surface-nanofabrication using probe oxidation is presented. Electrochemically generated oxide nano ridge structures can be fabricated using probes for atomic force microscopy. Moreover, removing the oxide ridge by hydrofluoric acid etching can also produce nanogroove structures. The relationship between the nanostructure shapes and fabrication conditions such as applied voltage and radius of curvature of the probe was investigated. The height of the oxide ridge can be controlled with sub-nanometer accuracy by the applied voltage and the width can be controlled by the tip radius. The depth and width of the groove can be controlled by adjusting the height and width of the ridge. Nanostructures with a very small height or depth (about 50 nm wide and < 1 nm high or deep) can be fabricated by our method. This is very useful for clarifying the nanotribology of micro- or nanomechanical devices.     

Microelectromechanical Resonator Characterization Using Noncontact Parametric Electrostatic Excitation and Probing

A noncontact electrostatic probing technique using a scanning probe microscopy cantilever is shown to actuate and detect the resonant behavior of a micromachined resonator. The method is capable of characterizing a resonator with resonant frequency much greater than that of the cantilever. The coupled oscillator model developed for this system describes the resonant response of the test resonator as detected through the probe, including the fourth-power dependence on the probe drive voltage. The veracity of this model is demonstrated through comparison with experimental data obtained from a test resonator with a resonant frequency ten times greater than the resonant frequency of the probe cantilever. This technique yields a straightforward determination of the resonant frequency and quality factor of a micromachined resonator, avoiding limitations due to optical interference and any reliance on a supporting circuitry.     

High-speed imaging by electromagnetic alloy actuated probe withdual spring

This paper describes a magnetically actuated cantilever with dual spring (cantilevered actuator and torsional cantilever) for a high-speed imaging of atomic force microscopy (AFM). A fabricated cantilever beam with a high resonant frequency is successfully actuated by electromagnetic force. A planar coil is placed on the free end of the cantilever beam and embedded in a groove formed on the silicon cantilever to get a large deflection. Static and dynamic mechanical characteristics of the fabricated probes have been measured. The experimental results of the mechanical properties are compared with the calculation results obtained from a finite element method. When flowing a current of ±10 mA, a static deflection of ±2 can be achieved by a cantilever with a length of 400 μm. The scanning speed of AFM is increased up to 1 mm/s by actuating the high resonant frequency cantilever in constant force mode     

Fabrication of improved piezoresistive silicon cantilever probes for the atomic force microscope

This paper describes an improved design for a monolithic silicon atomic force microscope (AFM) probe using piezoresistive sensing. The probe is V shaped, with a sharp tip at the free end and two piezoresistors at the root, and is fabricated using silicon-on-insulator (SOI) starting material. The maximum sensitivity of the AFM probe is measured to be 4.0(± 0.1) × 10⁻⁷ Å⁻¹, which is larger than that of the previous parallel-arm piezoresistive AFM probe. The measured results are in reasonable agreement with the values predicted by theory. The minimum detectable force and minimum detectable deflection of the AFM probes are predicted to be 1.0 × 10⁻¹⁰ N and 0.29 Å_r.m.s., respectively, using a Wheatstone bridge arrangement biased at a voltage of ± 5 V and bandwidth of 10 Hz–1 kHz.     

Analysis of dynamic sensing of force between a probe and a vibrating sample for purposes of atomic force microscope

Using a perturbation method, we study the influence of the vibration of the sample on the resonance curve of a probe. The obtained resonance curve indicates that both the resonance frequency shift and the vibration amplitude of the probe are proportional to the gradient of the interaction force between the probe and the sample, even if the probe is not forced to vibrate by an external force. For several surface forces such as the Casimir force, which are described by power functions, we show that the frequency shifts obtained by the perturbation method agree well with those obtained by numerical simulations.     

基于应变式传感器的压电陶瓷定位系统设计

基于压电陶瓷驱动的纳米扫描和定位系统,是原子力显微镜系统的关键部件。本文设计了基于电阻式应变传感器(SGS）的压电陶瓷微纳米位移定位系统。该系统在硬件上采用仪表放大器对SGS应变信号进行RF滤波、放大、模拟滤波处理得到与压电陶瓷位移变化线性相关的电压信号,该信号由高精度AD采集,并通过控制器输出到上位机软件MATLAB中进行噪声分析、FIR数字滤波去噪、线性度分析。实验结果表明,该位移检测系统输出电压噪声峰峰值小于0.5mV,输出非线性误差小于0.06%,可实现2nm的位移分辨率。该定位系统可以应用于原子力显微镜的开发中。     

Fabrication of AFM probe with CuO nanowire formed by stress-induced method

A novel method has been proposed to fabricate an atomic force microscope (AFM) probe using CuO nanowire and a stress-induced method that can form the nanowire easily. By heating a commercial AFM probe with a film coating of Ta and Cu, a Cu hillock with CuO nanowires on its surface could be formed at the end of the probe. The thickness of the coating films, the heating temperature, and the heating time were investigated to obtain CuO nanowires with a high aspect ratio for use as an AFM probe tip. It was found that a suitable probe tip can be fabricated using the a Cu film thickness of 700 nm, a heating temperature of 380 °C and a heating time of 6 h. Probe tips (~5 μm high) and nanowires of ~25 nm diameter were obtained successfully. In the range evaluated, the measurement resolution of the CuO nanowire probe was slightly worse than that of a commercial AFM probe. However, both probes had almost the same dimensional measurement precision.     

Nanopositioning for storage applications

In nanotechnology applications, nanopositioning, i.e., nanometer-scale precision control at dimensions of less than 100 nm, plays a central role. One can view nanopositioners as precision mechatronics systems aiming at moving objects over a certain distance with a resolution that could be as low as a fraction of an Ångström. Actuation, position sensing and feedback control are the key components of nanopositioners that determine how successfully the stringent requirements on resolution, accuracy, stability, and bandwidth are achieved. Historically, nanopositioning has played a critical role in scanning probe microscopy (SPM), and it appears that it will play a crucial role in emerging applications such as lithography tools and semiconductor inspection systems, as well as in molecular biology, nanofabrication, and nanomanufacturing. Moreover, it is becoming an important requirement in storage systems, ranging from novel probe-based storage devices to mechatronic tape-drive systems, to support the high areal density or storage capacity needs. This paper will review control-related research in nanopositioning for two extreme cases of data-storage systems, namely, in probe and in tape storage.     

A comparison of scanning methods and the vertical control implications for scanning probe microscopy

This article compares the imaging performance of non‐traditional scanning patterns for scanning probe microscopy including sinusoidal raster, spiral, and Lissajous patterns. The metrics under consideration include the probe velocity, scanning frequency, and required sampling rate. The probe velocity is investigated in detail as this quantity is proportional to the required bandwidth of the vertical feedback loop and has a major impact on image quality. By considering a sample with an impulsive Fourier transform, the effect of scanning trajectories on imaging quality can be observed and quantified. The non‐linear trajectories are found to spread the topography signal bandwidth which has important implications for both low and high‐speed imaging. These effects are studied analytically and demonstrated experimentally with a periodic calibration grating.     

Direct Fabrication of Nanoscale Light Emitting Diode on Silicon Probe Tip for Scanning Microscopy

We have fabricated a silicon microprobe integrated with a nanometer-sized light emitting diode (Nano-LED) on the tip. This paper describes the fabrication procedure and preliminary topographic testing results. The silicon probe with electrode pattern was made by wet-etching a silicon-on-insulator wafer using oxide as the mask. Subsequently, the probe tip was cut using a focused ion beam (FIB) to form a 150 nm-wide gap. Semiconductor nanoparticles (CdSe/ZnS core-shell nanoparticles) were electrostatically trapped and excited within the electrode gap made on the probe tip. The LED-tip is approximately 150 nm 150 nm. The nano-LED light intensity and current were measured as a function of the driving voltage up to 25 V. In addition to the electroluminescence peaks from the CdSe particles, possible emission from silicon dioxide doped in the FIB milling process was also observed in the measured spectra. Basic mechanical characteristics of the silicon probe were measured by mounting the probe on a tuning fork in a standard near-field scanning optical microscopy (NSOM) set up. It was observed that the drag force reduces the probe oscillation as the vibrating tip approached the near-field of the sample surface. The topographic images of a chromium test pattern on a glass substrate were successfully acquired by keeping the probe tip within roughly 5 nm from the sample surface. Although the probe tip shape and the location of the Nano-LED are yet to be further optimized before realizing near-field optical scanning experiment, the result showed its great promise as a new type of NSOM tip with the ldquoon-proberdquo light-source.     

Integrated design of the feedback controller and topography estimator for atomic force microscopy

In atomic force microscopy (AFM) the force between the measurement tip and the sample is controlled in a feedback loop to prevent damage of the tip and sample during imaging, and to convert the measurement of the tip–sample force into an estimate of the sample topography. Dynamical uncertainties of the system limit the achievable control bandwidth and the accuracy of the topography estimation. This paper presents an integrated approach to design a feedback controller and topography estimator, taking into account the dynamical uncertainties of the system. The proposed methodology is experimentally demonstrated on a commercial AFM system, showing a direct trade-off between the control bandwidth and the accuracy of the topography estimation.     

Design and batch fabrication of probes for sub-100 nm scanningthermal microscopy

A batch fabrication process has been developed for making cantilever probes for scanning thermal microscopy (SThM) with spatial resolution in the sub-100 nm range. A heat transfer model was developed to optimize the thermal design of the probes. Low thermal conductivity silicon dioxide and silicon nitride were chosen for fabricating the probe tips and cantilevers, respectively, in order to minimize heat loss from the sample to the probe and to improve temperature measurement accuracy and spatial resolution. An etch process was developed for making silicon dioxide tips with tip radius as small as 20 nm. A thin film thermocouple junction was fabricated at the tip end with a junction height that could be controlled in the range of 100-600 nm. These thermal probes have been used extensively for thermal imaging of micro- and nano-electronic devices with a spatial resolution of 50 nm. This paper presents measurement results of the steady state and dynamic temperature responses of the thermal probes and examines the wear characteristics of the probes     

Experimental study on band merging of non-linear multi-band piezoelectric energy harvester into single broadband using magnetic coupling

The operational bandwidth of Vibration Energy Harvesters (VEH) is area of concern due to stochastic, time-varying, random and multi-frequency nature of available environmental vibrating sources. Most of the VEH have narrow bandwidth providing usable power at specific frequencies. Efforts have been made to increase the frequency range by introducing non-linear structures and techniques. In this paper, multi-band output of the non-linear Piezoelectric Energy Harvester (PEH) is transformed into single wider band output using additional non-linear phenomenon. Dual region operation of PEH results into two separate band output. First region is the outcome of beam resonance and Centre of Gravity (CoG) shift whereas second region is due to the non-linear behaviour of cylinders. In this work, these separate bands are merged to form a single wider band. For merging these two bands and enhancing the bandwidth of PEH, additional phenomenon is introduced using two permanent magnets. A varying magnetic field by changing the distance between magnets changes stiffness of the cantilever beam and that leads to a change in the resonant frequency of band-I. Thus, the overall process shifts band-I towards band-II. In this work, the two separate bands are merged to have one wider band providing 53.22% more frequency coverage than our previous work with a bandwidth of 47.5 Hz. This band includes vibrational frequency range of 25.65–73.15 Hz at 1.4 g acceleration. Cylinder material and its effect with magnetic interaction is also studied. The magnetic force between two permanent magnets is measured experimentally. Effect of magnetic force on centre resonant frequency of beam is compared with experimental and simulated results. Effect of magnetic force on bandwidth of the device is studied.

     

A microwave probe nanostructure for atomic force microscopy

An atomic force microscope (AFM) probe on a GaAs wafer was studied as a new microwave probe structure. A waveguide was created by evaporating an Au film on the top and bottom surfaces of the GaAs AFM probe. The fabricated AMF probe’s tip is 8 μm long and has a radius of curvature of about 50 nm. The open structure of the waveguide at the tip of the probe was generated by using focused ion beam (FIB) fabrication. AFM topography of a grating sample was created by using the fabricated microwave AFM probe. The fabricated probe exhibits nanometer-scale resolution, and microwave emission was successfully detected at the tip of the probe by approaching Cr–V steel and Au wire samples.